The invention relates to a corona ignition system and to a method for controlling a corona ignition system.
US 2011/0114071 A1 discloses a corona ignition system with which a fuel/air mixture in a combustion chamber of an internal combustion engine can be ignited by a corona discharge produced in the combustion chamber. This corona ignition system has an ignition electrode, which protrudes from an insulator. The ignition electrode, the insulator and a sleeve surrounding the insulator form an electrical capacitor. This capacitor is part of an electrical oscillating circuit of the corona ignition device. The oscillating circuit is excited with a high-frequency AC voltage for example from 30 kHz to 50 MHz causing a voltage excess at the ignition electrode so that a corona discharge forms at the ignition electrode.
The high-frequency AC voltage is produced by a high-frequency generator. The input voltage of the high-frequency generator is produced by a converter from the on-board supply voltage of the vehicle. The input voltage of the high-frequency generator generally lies in the range from 100 V to 400 V in the case of known corona ignition systems.
A corona discharge forms ions and radicals in a fuel/air mixture in the combustion chamber of an engine. When a critical concentration of ions and radicals is reached, the fuel/air mixture ignites. The rate at which ions and radicals are produced is dependent on the size of the corona discharge and the electrical power thereof. The size and power of a corona discharge can only increase up to a critical limit. If this limit is exceeded, the corona discharge transitions into an arc discharge or spark discharge.
For this reason corona ignition systems are controlled such that the corona discharge is as large as possible, but a breakdown of the corona discharge into an arc or spark discharge is avoided. The fuel/air mixture can then be ignited as quickly as possible and the ignition moment can thus be predefined as precisely as possible.